Search

The undesirable photorefractive properties inherent in materials like LiNbO3 and LiTaO3 seriously limit the usefulness of these waveguides, particularly for visible wavelength operation where the high intensities within the guides cause catastrophic damage. The U.K. team reports a new approach whereby ion-beam implantation is used as a post-processing technique that reduces the photorefractive effect in previously fabricated annealed proton exchange channel waveguides in LiNbO3. The researchers say ion-beam implantation dramatically decreased the time dependent transmission losses implying that photorefractivity was greatly reduced. This result is significant, they add, because it provides a simple method for producing non-photorefractive LiNbO3.

Photo refractive planar waveguides have been fabricated in cerium doped Strontium Barium Niobate (SrxBa(1-x)Nb2O6 : SBN) single crystals by ion beam implantation. The losses measured were as low as 0.1 dB /cm and 7.0 dB /cm for the TM and TE modes respectively. Subsequent two beam coupling experiments performed on the waveguides showed that, unlike BaTiO3 and KNbO3 waveguides formed by ion beam implantation, the two-beam coupling gain direction did not reverse. The response time had also been reduced by two orders of magnitude.

Planar waveguides have been fabricated in SBN:61 and SBN:75 by ion-beam implantation. The implantation was carried out using 2.0MeV H+ ions with doses ranging from 2x10 for the TE mode. These losses are significantly lower than those observed for planar waveguides fabricated previously using sulphur diffusion [1]. Two beam coupling experiments were then carried out on the SBN waveguide where it was observed that the gain direction was the same as that of the bulk crystal. Previously, in both BaTiO3 [2] and KNbO3 [3] planar waveguides fabricated in the same manner, the gain direction for two beam coupling had been shown to reverse. This phenomenon may be due to the ion beam implantation process reducing the waveguide layer and subsequently changing the ratio of impurity atom oxidation states - in the case of BaTiO3, the ratio of Fe2+:Fe3+. It is thought that the predominant photoexcited charge carrier in both BaTiO3 and KNbO3 is changed from the hole to the electron whereas in SBN, the electron remains the predominant carrier even after the implantation process. Modelling of these effects has been undertaken, giving an explanation of why gain reversal should occur in certain photorefractive planar waveguides fabricated by ion-beam implantation. This paper will discuss the gain and response time of the SBN waveguide in comparison to the bulk and the theoretical predictions of the effects of ion-beam implantation on photorefractive materials.

Crystalline and stoichiometric thin film of Gd3Ga5O12, have been deposited onto heated Y3Al5O12, substrates by a pulsed laser deposition technique. The refractive indices of the films are in excellent agreement with the bulk crystal.

We report two methods of producing planar technology waveguides for low threshold laser operation. Ion-implantation can make waveguides in many materials with waveguide laser operation so far observed in YAG, GGG, YAP, LiNbO3, BGO and glass, doped with Nd3+, Yb3+, and Tm3+. 2D and 3D guides have been fabricated and propagation losses as low as 0.15dB/cm can be obtained. Liquid-phase epitaxial thin film growth has so far produced Nd3+ and Yb3+ doped YAG, 2D waveguide lasers. Extension to new materials and production of 3D guides is currently under consideration. These guides have losses as low as 0.05dB/cm and have potential both as low threshold longitudinally pumped lasers and high average power side pumped devices.

Yb:YAG has manv advantages compared to the widely used Nd:YAG system. These include closer pump and laser wavelengths, leading to a more efficient transfer of energy from the pump to laser photons and less thermal loading of the gain medium. Excited state absorption, upconversion, and concentration quenching are also reduced because of the fact that there is only one excited 4f manifold. Efficient, room-temperature operation of a bulk Yb:YAG laser at 1.03 µm has recently been reported showing that the broad absorption bands are well suited to diode pumping.

Optical confinement within a planar waveguide structure in BaTiO3 produces significant decreases in the response times of two-wave mixing, self-pumped and mutually-pumped phase conjugation.

Self-pumped and mutually-pumped phase conjugator configurations have been demonstrated in a planar waveguide in BaTiO3, fabricated by the technique of ion implantation. For equal input powers a two order of magnitude decrease in response time is observed in the waveguide as compared to the bulk.

The main advantage of using waveguides in laser systems is that they produce high pump intensities over long interaction lengths for low input pump powers. This should lead to lower thresholds and more efficient lasers. Often though extra loss due to waveguide propagation reduces the benefits of this confinement. However in three-level and quasi-three-level laser systems there already exists absorption loss at the laser wavelength due to thermal population of the lower laser level. Any added waveguide propagation loss will therefore not have such a significant effect on laser performance. An example of such a laser system is Yb:YAG where 4% of the total population resides in the lower laser level. For a 6.5 at.% doped sample this is roughly equivalent to a propagation loss of 2.5db/cm which for the guides discussed here is the main contribution to the loss. The laser performance of Yb:YAG has been measured in planar waveguides made by two methods - ion-implantation and epitaxial growth.

Ion implantation, which can create waveguides in a wide range of materials, has been used to produce very low threshold channel waveguide lasers.

We report what we believe to be the first laser operation of channel waveguides formed in Nd-doped crystals by high energy ion implantation. Recently, there has been much interest shown in the fabrication of waveguides by various methods in crystal laser hosts.

Ion implantation is a very useful technique which can be used to modify the optical properties of insulators. In particular, much interest has been caused by the ability to create a refractive index profile so that optical waveguides and integrated optical devices can be fabricated. A large amount of work has been carried out on crystals such as LiNbO3 which is of interest due to its high electrooptic coefficient. However, due to the physical nature of the ion implantation process, refractive index changes and hence optical waveguides can be created in a wide range of crystals. This raises the possibility of creating waveguides in very many interesting solid state laser systems, and such waveguides have potentially very low thresholds for laser operation if the guide losses and other cavity loss mechanisms can be kept small.